Metalworking system with force controlled wire feed start operation

ABSTRACT

A method for controlling a start of a metalworking operation. The method includes detecting an initial contact between a wire being fed from a welding apparatus and a workpiece and, in response to the detection, halting feeding of the wire from the welding apparatus. The method further includes activating a high energy heat source configured to heat a tip of the wire and resuming the feeding of the wire from the welding apparatus when the tip of the wire is heated by the high energy heat source to a plastic state. The feeding of the wire is resumed by measuring a force feedback from the wire contacting the workpiece. An apparatus for implementing the method is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to concurrently filed and commonly assignedpatent application Ser. No. ______, bearing attorney docket number09794624-000565 and entitled “Metalworking System With Force Control,”which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to metalworking equipment andmethods, and more specifically to welding, cladding and additivemanufacturing control systems.

BACKGROUND

Hot wire welding and cladding are processes where a metal filler wire isresistively heated, typically, to a softened or plastic or semi-liquidusstate, usually by passing an electrical current through it. This reducesthe amount of added heat from another source needed for the base metalof a workpiece to which the heated wire is applied. The wire istypically fed in front of or behind a high-power energy source such as alaser or plasma that further melts the wire material, often along withthe base metal of the workpiece, to produce a weld or clad. This puddlecan also be referred to as the welding or cladding spot.

Wire feeders are used in various welding and cladding applications tofeed the wire to the welding or cladding spot. Such wire can be referredto as filler wire, additive wire or consumable wire.

During operation, the wire is fed into or near the puddle. This way,when a workpiece is moved relative to the welding or claddingarrangement (with either the workpiece moved or the welding or claddingequipment moved), the puddle can be maintained to create a continuousweld or cladding layer.

In hot wire welding, the start of wire feeding is sequenced veryprecisely to prevent arcing, or overfeeding of the wire before theprocess can stabilize and be in a steady state. Commonly, first the wirefeed is initiated. Second, the wire contacts the workpiece. Third,heating power (e.g., electrical current applied through the wire, whichhas some resistance) is applied to the wire. Fourth, the wire heats to asoftened/plastic/semi-liquidus phase at the weld/clad spot, namely theweld/clad puddle. Fifth, feeding and sustained high power energy heatingof the wire occurs in the steady state.

The use of hot wire welding, such as tungsten inert gas welding, tendsto be more part-related and industry-related. For example, hot wire TIGis used extensively in the transportation and power generationindustries. It's big in shipbuilding, and for rebuilding turbine shaftsfor large power plants. Hot wire TIG also is used in cladding very largevalve welds such as those for oil industry in which welders clad theinside of the valve weld with high-performance alloys.

Current hot wire welding and cladding machines rely on welding voltageand current to control the process of resistively heating a wire. Theseparameters may also be used to calculate power, resistance, andextension. It is important to control the resistive heating process sothat the wire is heated to sufficient temperature but also so that anarc is not generated between the wire and the workpiece. The temperatureof the wire should be high enough that the wire plastically deforms atits end. However, if the temperature is too high, the end of the wirewill turn liquid and electromagnetic pinch forces can cause an arc to beestablished. Arcing will disrupt the precise resistive heating goinginto the wire, can cause inconsistencies throughout the weld, and willrequire eye protection from the arc rays. Arcing can also be detrimentalto cladding processes by causing considerable base metal melting, thusinfluencing the dilution of the cladding. The process of starting thewelding or cladding operation is particularly prone to arcing.

When controlling the hot wire process to avoid arcing by relying onvoltage and current feedback, information about the particular type ofwire that is being used is necessary. Since different wire types havedifferent parameters, such as melting temperature, electricalresistivity, heat capacity, and thermal conductivity, each wire typerequires its own program or input of particular parameters into thewelding or cladding machine in order to ensure successful operation.

SUMMARY

Embodiments of the present disclosure employ force feedback from thewire to control a metalworking operation. The force feedback is providedby means of a signal indicative of a force on the wire. When feeding toair, i.e., when the wire encounters no obstacle, the force should bezero or null. When the wire encounters a fixed obstacle such as aworkpiece, the force, absent a change in the exertion of the feedermechanism used to feed the wire, will essentially be the counter forceto that exerted by the feeder mechanism. The force feedback can bedetected as a change in a force signal indicative of the force feedbackor as a force error resulting from a force outside of a predeterminedforce threshold.

As used herein, a metalworking operation means and includes a weldingoperation, a cladding operation and an additive manufacturing operation.A hotwire is a wire that is preliminarily heated, typically resistively,to a softened state during application of the wire in an operation.Thereafter, a high energy source is applied to the wire or the wire andthe workpiece, to melt the wire or the wire and a portion of theworkpiece, respectively. An additive manufacturing operation uses moltenwire to deposit metal to produce products. An example of an additivemanufacturing process is what can be referred to as 3-D printingprocesses.

In an embodiment of using wire force feedback during the start of themetalworking operation, a controlled start is achieved and arcing isavoided by preheating the end of the wire and using force feedbackinstead of, or in addition to, voltage and current feedback.

In an embodiment, a method for controlling a start of a metalworkingoperation is provided. The method includes detecting an initial contactbetween a wire being fed from a feeder apparatus and a workpiece and, inresponse to the detection, halting feeding of the wire from the feederapparatus. The method further includes activating a high energy heatsource configured to heat a tip of the wire and resuming the feeding ofthe wire from the feeder apparatus when the tip of the wire is heated toa softened state. The softened state will result from either thepreliminary heating of the wire, the onset of melting of the wire by thehigh power energy source, or a combination of both. The feeding of thewire is resumed by in accordance with a force feedback from the wirecontacting the workpiece.

In an embodiment there is provided a method for controlling a start of ametalworking operation comprising: detecting an initial contact betweena wire being fed from a wire feeding apparatus and a workpiece; inresponse to the detection, halting feeding of the wire from the wirefeeding apparatus; with the wire in contact with the workpiece,activating a high energy heat source configured to heat a tip of thewire to a softened state; and after application of the high energy heatsource is activated, resuming the feeding of the wire from the wirefeeding apparatus, wherein, the feeding of the wire is resumed inaccordance with a force feedback from the wire contacting the workpiece.

In an embodiment, after initial contact of the wire with the workpieceand prior to activating the high energy heat source configured to heat atip of the wire to a softened state, the wire is subjected topreliminary heating with another energy source.

In an embodiment, after initial contact of the wire with the workpieceand prior to activating the high energy heat source configured to heat atip of the wire to a softened state, the wire is subjected to resistiveheating with another energy source.

In an embodiment, the initial contact is detected based on the forcefeedback.

In an embodiment, the plastic state is detected when the force feedbackfrom the wire is reduced below a force corresponding to the detection ofthe initial contact.

In an embodiment, the high energy heat source is a laser.

In an embodiment, the high energy heat source is a plasma.

In an embodiment, the method further includes determining, by circuitryincluding a control circuitry, a force error for the force feedbackbased on a predetermined force threshold; and adjusting, by thecircuitry, a heating of the wire, a feed rate of the wire, or both basedat least in part on the force error when the force error is outside ofthe predetermined force threshold.

In an embodiment, the control circuitry implements a constant torquecontrol scheme.

In an embodiment, the method further includes maintaining, by thecircuitry, a constant wire feed speed after resuming the feeding of thewire.

In an embodiment, the force feedback is measured directly via a forcemeasurement device.

In an embodiment, the force feedback is inferred based on a change in afeed motor current of the wire feeding apparatus.

In an embodiment, the control circuitry varies the feed motor current tomaintain a constant wire feed speed.

In an embodiment, the method further includes increasing, by circuitryincluding control circuitry, the heating of the wire when the forceerror is above the predetermined force threshold; and decreasing, by thecircuitry, the heating of the wire when the force error is below thepredetermined force threshold.

In an embodiment, there is provided a non-transitory storage medium inwhich there is stored program instructions which when executed by aprocessor effect any of the method embodiments described above. In anembodiment, a metalworking apparatus is provided. The apparatus includesa wire feed mechanism configured to feed a wire from a wire feeder ontoa workpiece and a heating power supply configured to supply a heatingcurrent to the wire contacting the workpiece. The apparatus furtherincludes a control circuitry configured to (a) detect an initial contactbetween the wire being fed from the wire feeder and the workpiece, (b)in response to the detection, halt feeding of the wire from the wirefeeder, (c) activate a high energy heat source configured to heat a tipof the wire, and (d) resume the feeding of the wire from the welding gunwhen the tip of the wire is heated by the high energy heat source to asoftened state. In the disclosed apparatus, the feeding of the wire isresumed in accordance with a force feedback from the wire contacting theworkpiece.

In an embodiment, there is provided a metalworking apparatus comprising:a wire feed mechanism configured to feed a wire from a gun onto aworkpiece; a heating power supply configured to supply a heating currentto the wire; and circuitry configured to (a) detect an initial contactbetween the wire being fed from the welding gun and the workpiece, (b)in response to the detection, halt feeding of the wire from the weldinggun, (c) activate a high energy heat source configured to heat a tip ofthe wire, and (d) resume the feeding of the wire from the welding gunwhen the tip of the wire is heated by the high energy heat source to aplastic state, wherein, the feeding of the wire is resumed in accordancewith a force feedback from the wire contacting the workpiece.

In an embodiment of the apparatus, the initial contact is detected basedon the force feedback.

In an embodiment of the apparatus, the softened state is detected whenthe force feedback from the wire is reduced below a force correspondingto the detection of the initial contact.

In an embodiment of the apparatus, the high energy heat source is alaser.

In an embodiment of the apparatus, the circuitry is further configuredto: determine a force error for the force feedback based on apredetermined force threshold; and adjust the heating current used toheat the wire based at least in part on the force error when the forceerror is outside of the predetermined force threshold.

In an embodiment of the apparatus, the circuitry is further configuredto maintain a constant wire feed speed or constant ramp rate inconnection with resuming the feeding of the wire.

In an embodiment, the circuitry implements a constant torque controlscheme.

In an embodiment of the apparatus, a force measurement device thatdirectly measures the force feedback.

In an embodiment of the apparatus, the force feedback is inferred basedon a change in a feed motor current of the wire feed mechanism.

In an embodiment of the apparatus, the circuitry is further configuredto vary the feed motor current to maintain a constant wire feed speed.

In an embodiment of the apparatus, the circuitry is further configuredto: increase the heating current when the force error is above thepredetermined force threshold; and decrease the heating current when theforce error is below the predetermined force threshold.

These and other features and aspects are described below in the detaileddescription of the preferred embodiments with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure can be better understood by referring to thefollowing figures. The components in the figures are not necessarily toscale, emphasis instead being placed upon illustrating the principles ofthe disclosure. In the figures, reference numerals designatecorresponding parts throughout the different views.

FIG. 1 is a diagram illustrating an exemplary welding system environmentin which an embodiment of the present disclosure may operate.

FIG. 2 is a diagram illustrating another exemplary welding systemenvironment in which an embodiment of the present disclosure mayoperate.

FIGS. 3-4 are block diagrams illustrating a hot wire operation of thewelding system of FIG. 1 in further detail, according to an embodiment.

FIG. 5 is a flow chart illustrating a method of force control operationof the welding system of FIG. 1, according to an embodiment.

FIG. 6 is a flow chart illustrating another method of force controloperation of welding system of FIG. 1.

FIG. 7 is a flow chart illustrating a method of force control startoperation of the welding system of FIG. 1, according to an embodiment.

FIG. 8 illustrates in block diagram form a control arrangement.

FIG. 9 illustrates another control arrangement.

DETAILED DESCRIPTION

The present disclosure is herein described in detail with reference toembodiments illustrated in the drawings, which form a part hereof. Otherembodiments may be used and/or other changes may be made withoutdeparting from the spirit or scope of the present disclosure. Theillustrative embodiments described in the detailed description are notmeant to be limiting of the subject matter presented herein.

Reference will now be made to the exemplary embodiments illustrated inthe drawings, and specific language will be used herein to describe thesame. It will nevertheless be understood that no limitation of the scopeof the invention is thereby intended. Alterations and furthermodifications of the inventive features illustrated herein, andadditional applications of the principles of the inventions asillustrated herein, which would occur to one skilled in the relevant artand having possession of this disclosure, are to be considered withinthe scope of the present disclosure.

Referring to FIG. 1, a hot wire metalworking system 100 is shown.Although referred to herein mostly as a welding or cladding system, itcan be understood that the principles disclosed herein are equallyapplicable to an additive manufacturing process, given the similarfeeding of wire and the application of cladding principles to build uplayers of metal from the wire to produce a product.

As discussed in further detail below, the system 100 uses force feedbackfrom the wire to control the welding or cladding operation throughoutthe entire process. Since the force generated by the wire with plasticdeformation at the tip is substantially similar among different wiresand wire types, using force feedback from the wire to control theprocess eliminates or significantly reduces the need to change controlprograms governing the operation of the welding apparatus, as well asthe need to enter specific wire parameters when changing wires.

In the illustrated embodiment, the system 100 includes a weldingapparatus 102 (also representative of a cladding or additivemanufacturing apparatus) having a gun 104. The apparatus 102 furtherincludes an electric motor 106 that feeds the wire 108 onto theworkpiece 110. The motor 106 operates drive rolls 112 that feed the wire108 through the gun 104. The wire 108 is heated by a resistive heatingpower supply 114, which applies resistive heating current to the wire108 contacting the workpiece 110. In various embodiments, the resistiveheating power supply 114 is an AC or DC power supply controlled by acontrol circuitry 115 associated with the welding apparatus 102.Although the resistive heating power supply 114 and the controlcircuitry 115 are schematically illustrated as being external to thewelding apparatus 102, those skilled in the art will realize that thepower supply 114 and/or the control circuitry 115 may be either internalor external to the welding apparatus 102.

Those skilled in the art will understand that the control circuitry isrepresentative of various circuit configurations that can implement acontrol logic such as a proportional control, aproportional-integral-differential control or any other suitable controlthat uses a feedback signal to adjust an operating parameter. Further,the control circuitry 115 is representative of different circuitstructures for implementing such control logic, be it analog or digitalcontrol, and whether it be implemented using hardware, firmware,software or some combination of the foregoing. The control circuitry 115may include a processor to execute program code which is stored in aseparate non-transitory memory device or integrated into the processorchip itself.

Further, those skilled in the art will also understand that although aresistive heating arrangement is described, other methods andarrangements can be used such as heat sources.

In embodiments, the force from the wire 108 may be determined orindicated by various devices including a force measuring device, such asa load cell transducer built into the gun 104 or by using a stand-aloneapparatus that directly measures the force. A dynamometer can beattached to the feeder motor shaft and torque exerted by the feedermotor can be measured. Additionally, a suitable speed sensor can be usedto measure motor shaft or feeder drive wheel speed, with speedcorrelated to the amount of torque exerted by the motor.

In other embodiments, the force from the wire 108 may be inferred fromanother measurement, such as the wire feed motor current, thatindirectly measures the force. In one embodiment, the current that issent to the motor of the feeder 106 varies to maintain a constant wirefeed speed. If there is a large force at the end of the wire 108,pushing back in the direction of wire travel, the motor of the feeder106 will need an increase in the current to be able to keep feeding thewire 108 forward at the desired constant speed. Based on the variationsin the wire feed current supplied to the motor 106, a force at the wiretip can be inferred. Methods and circuitry for reading motor currentsare well known, as are methods and circuitry for detecting increase inmotor current due to, e.g., counter forces on the rotation of the shaftof the motor.

In FIG. 2, a load cell 140 is illustrated position between one end ofthe feeder 106 and a surface 142. It can be appreciated that the feederwould be permitted some movement to allow a force to be registered bythe load cell 140 as the feeder 106 is forced back against the surface142.

The force measurement, whether direct or indirect, is used to determinean error from a predetermined force set point. Based on the force error,a resistive heating current supplied to the wire 108 is adjusted.Optionally, the adjustment in the resistive heating current takes intoaccount a predetermined system gain factor. In an embodiment, the gainfactor represents a correction value associated with system responsetime. As further shown in FIGS. 3-4, an increase in resistive heatingcurrent raises the temperature in the wire 108 and makes plasticdeformation 120 at wire tip 116 easier, which results in a lower forcereading. A decrease in resistive heating current lowers the temperaturein the wire 108 and makes plastic deformation 120 more difficult, whichresults in a larger force reading.

To achieve a controlled start of the welding or cladding operation, anend 116 of the wire 108 is preheated with a high energy heat source,such as a laser 118. Wire force feedback is then used instead of, or inaddition to, voltage and current feedback to achieve a controlled startand prevent arcing, as described in further detail below.

Thus, in accordance with principles disclosed herein, the gun 104 andlaser 118 are aligned so that the wire 108 will touch the workpiece justahead or just inside the advancing edge of where the laser 118 would hitthe workpiece, Then the start of the hotwire process starts with thewire 108 feeding toward the workpiece. When it is sensed, by a forcefeedback (direct or indirect), voltage feedback or both, that the wire108 is touching the workpiece, the wire feeding is stopped and a levelof current is applied so that the majority of the wire 108 does not heatto a point where it loses its stiffness. Then the laser 118 (or otherhigh intensity energy source) is turned on. The wire is stationary for agiven period of time to let the end of the wire heat up to a plasticstate. After the time period to get the end of the wire in the plasticstate is up, the wire feed speed is ramped up to the final steady statewire feed speed. During the ramping up of the wire feed speed, if thedetected force is above a threshold or limit, either the wire feed speedramp is slowed or the welding current is increased to return to thedesired force. The force is set to a level which correlates to the endof the wire plastically deforming.

Referring to FIG. 5, an embodiment of a method for hot wire welding andcladding using wire force feedback is shown. In step 400, the weldingapparatus control circuitry 115 obtains a measurement of force feedbackfrom the wire 108. As discussed above, the force feedback from the wire108 may be measured directly via a force measuring device, such as adynamometer or a load cell transducer built into or otherwise connectedto the welding apparatus 102, or it may be inferred based on thevariation in the wire feed current required by the motor 106 to keep thewire feed speed constant. In step 402, the control circuitry 115determines an error in the force feedback reading with respect to apredetermined force feedback set point or threshold range that, forinstance, corresponds to the state of plastic deformation at the wiretip 116. In step 404, if the force error is within the predeterminedforce error threshold range, the method returns to step 400. Otherwise,in steps 404-406, if the force error is outside of a predeterminedthreshold, the control circuitry 115 either increases or decreasesresistive heating current applied to the wire so as to correspondinglyincrease or decrease the wire temperature to ensure plastic deformationat the tip 116, while preventing the tip 116 of the wire 108 frombecoming liquid. For example, a force error determination that is abovethe predetermined threshold indicates that the temperature of the wire108 needs to be increased to facilitate plastic deformation at the tip116. On the other hand, a force error determination below thepredetermined threshold indicates that wire temperature needs to bedecreased to prevent the tip 116 from becoming liquid. Alternatively orin addition, the control circuitry 115 varies one or more of the wirefeed speed and power output of the laser 118 in order to ensure plasticdeformation of the wire tip 116, while preventing it from turningliquid.

Referring to FIG. 6, another embodiment of a method for hot wire weldingand cladding using wire force feedback is shown. In FIG. 6, each overallloop could take place in a matter of microseconds or less, dependingupon the calibration of the feedback system. In step 420, the weldingapparatus control circuitry 115 obtains a measurement of force feedbackfrom the wire 108. As discussed above, the force feedback from the wire108 may be measured directly via a force measuring device, such as adynamometer or a load cell transducer built into or otherwise connectedto the welding apparatus 102, or it may be inferred based on thevariation in the wire feed current required by the motor 106 to keep thewire feed speed constant. In step 422, the control circuitry 115determines whether the force feedback has increased or is increasingrelative to a past measurement. Although not illustrated, the rate ofincrease could be determined as well, using, e.g., a series ofmeasurements, and the differences between. In step 424, if the forcefeedback is increasing, the wire heating current is increased to counterthe increased resistance. Then the process returns to step 420 foranother measurement.

However, if the force feedback has not increased or is not increasing,then the process proceeds to step 426 to determine if the force feedbackhas decreased or is decreasing. Although not illustrated, the rate ofdecrease could be determined as well, using, e.g., a series ofmeasurements, and the differences between. In step 426, if the forcefeedback is decreasing, the wire heating current is decreased to counterthe decreased resistance. Then the process returns to step 420 foranother measurement.

If the force feedback is neither increased/increasing nordecreased/decreasing, the process returns to step 420 for anothermeasurement.

Again, this process correspondingly increases or decreases the wiretemperature to ensure plastic deformation at the tip 116 whilepreventing the tip 116 of the wire 108 from becoming liquid.Alternatively or in addition, the control circuitry 115 can vary one ormore of the wire feed speed and power output of the laser 118 in orderto ensure plastic deformation of the wire tip 116, while preventing itfrom turning liquid.

Although not expressly depicted in the drawings, it may be desirable toinclude some hysteresis in the feedback and adjustment process avoidunnecessary or detrimental constant minor adjustments or to accommodateadjustment reaction times.

Referring to FIG. 7, an embodiment of a method for controlling a startof a hot wire welding or cladding operation is shown. In step 500, thegun 104 is aligned with a high energy heat source device, such as thelaser 118. In steps 502-506, the control circuitry 115 directs the motor106 to begin feeding the wire 108 toward the workpiece 110 until it hasdetermined that the wire 108 is touching the workpiece 110. In anembodiment, the control circuitry 115 determines the initial contact ofthe wire 108 with the workpiece 110 when a predetermined minimum wireforce feedback is detected or a voltage signal is detected. At thatpoint, in steps 508-510, the control circuitry 115 sets the resistiveheating current applied to the wire so that most of the wire extendingfrom the contact tip remains stiff and activates the laser 118. In step512, the wire 108 remains stationary until the tip 116 heats up to aplastic state. In an embodiment, a plastic state is achieved when thetip 116 is easily deformed, also known as the state of plasticdeformation. In one embodiment, the plastic state of the tip 116 isdetected when the force feedback from the wire is reduced from the forcecorresponding to detection of the initial contact to a predeterminedlower force threshold. Finally, once the wire tip 116 heats up to theplastic state, the control circuitry 115 directs the motor 106 to rampup the wire feed speed up to a steady state speed for the welding orcladding operation and controls the welding or cladding process via theforce feedback method discussed above in connection with FIG. 4.

In FIG. 8, there is illustrated a circuit arrangement in which controlcircuitry 800 is interconnected with at least one sensor transducer 802,a preliminary wire heater controller 804, a high power energy sourcecontroller 806 and a wire feeder motor controller 808. The controlcircuit 800 operates as described above to receive a force signalindicative of a force on the wire from the transducer 802 and to controloperation of the various controllers in accordance with the principlesdiscussed herein, namely, to start and/or adjust preliminary heating ofthe wire via appropriate signal to controller 804, start and/or adjustapplication of the high power energy to the wire via appropriate signalsto the controller 806, and start, stop and/or adjust the feed speed ofthe wire feeder motor via appropriate signals to the controller 808.

As illustrated, in an embodiment, the control circuitry 800 includes aprocessor 810 couple to an input/output section 812 via which signalsare input from and output to the transducer and the controllers. Logicexecuted by the processor is stored in the memory 814 logic executed bythe processor is stored in the memory 814 coupled to the processor 810.It can be appreciated that the logic can be in the form of software,firmware or hardware.

In FIG. 9, there is illustrated another control scheme. In this scheme,the energy delivered to the wire for heating (e.g., resistive heating)can be maintained at a constant level while the force exerted by thefeeder and/or the wire on the feeder is controlled. Feeder motor currentis used as a control variable in a force back loop. For this purpose,the following relationship is used:

$F_{wire} = {\frac{T}{r_{{drive}\mspace{14mu} {roll}}} - {\gamma\bigstar I}_{motor}}$

where T is the torque applied by the feed motor, r_(driveroll) is theradius of the drive roll of the wire feeder, γ is a constant, F_(wire)is the force on the wire, and I_(motor) is the wire feeder motorcurrent. In essence, this provides a constant torque feed system.

To that end, a force set point F_(wire set point) is compared to theforce feedback signal F_(fbk), which is either derived from a sensor,such as a load cell or dynamometer, or from the feeder motor currentI_(motor). The force feedback Ffbk is proportional to the motor currentImotor. In FIG. 9, the comparison is effected by a summation function F.

The output of the summation function F becomes the force feedback errorΣ_(force), which is equal to F_(fbk)−F_(wire set point). This outputΣ_(force) is feed into a proportional-integral-derivative (PID)controller C with appropriate filters and gains to generate a currentdifference output ΔI. This output ΔI is used to control the motor byadjusting feed motor command signal I_(motor), which in turn is used tocontrol the amount of current fed to the motor. This adjustment isaccomplished by increasing or decreasing the current fed to the motor,depending on the result of the summation as reflected in the signalI_(motor). For this the relationship isI_(motor(new))=I_(motor(old))+ΔI.

While various aspects and embodiments have been disclosed, other aspectsand embodiments are contemplated. The various aspects and embodimentsdisclosed are for purposes of illustration and are not intended to belimiting, with the true scope and spirit being indicated by thefollowing claims.

The foregoing method descriptions and the process flow diagrams areprovided merely as illustrative examples and are not intended to requireor imply that the steps of the various embodiments must be performed inthe order presented. As will be appreciated by one of skill in the artthe steps in the foregoing embodiments may be performed in any order.Words such as “then,” “next,” etc. are not intended to limit the orderof the steps; these words are simply used to guide the reader throughthe description of the methods. Although process flow diagrams maydescribe the operations as a sequential process, many of the operationscan be performed in parallel or concurrently. In addition, the order ofthe operations may be re-arranged. A process may correspond to a method,a function, a procedure, a subroutine, a subprogram, etc. When a processcorresponds to a function, its termination may correspond to a return ofthe function to the calling function or the main function.

The various illustrative logical blocks, modules, circuits, andalgorithm steps described in connection with the embodiments disclosedhere may be implemented as electronic hardware, computer software, orcombinations of both. To clearly illustrate this interchangeability ofhardware and software, various illustrative components, blocks, modules,circuits, and steps have been described above generally in terms oftheir functionality. Whether such functionality is implemented ashardware or software depends upon the particular application and designconstraints imposed on the overall system. Skilled artisans mayimplement the described functionality in varying ways for eachparticular application, but such implementation decisions should not beinterpreted as causing a departure from the scope of the presentinvention.

Embodiments implemented in computer software may be implemented insoftware, firmware, middleware, microcode, hardware descriptionlanguages, or any combination thereof. A code segment ormachine-executable instructions may represent a procedure, a function, asubprogram, a program, a routine, a subroutine, a module, a softwarepackage, a class, or any combination of instructions, data structures,or program statements. A code segment may be coupled to another codesegment or a hardware circuit by passing and/or receiving information,data, arguments, parameters, or memory contents. Information, arguments,parameters, data, etc. may be passed, forwarded, or transmitted via anysuitable means including memory sharing, message passing, token passing,network transmission, etc.

The actual software code or specialized control hardware used toimplement these systems and methods is not limiting of the invention.Thus, the operation and behavior of the systems and methods weredescribed without reference to the specific software code beingunderstood that software and control hardware can be designed toimplement the systems and methods based on the description here.

When implemented in software, the functions may be stored as one or moreinstructions or code on a non-transitory computer-readable orprocessor-readable storage medium. The steps of a method or algorithmdisclosed here may be embodied in a processor-executable software modulewhich may reside on a computer-readable or processor-readable storagemedium. A non-transitory computer-readable or processor-readable mediaincludes both computer storage media and tangible storage media thatfacilitate transfer of a computer program from one place to another. Anon-transitory processor-readable storage media may be any availablemedia that may be accessed by a computer. By way of example, and notlimitation, such non-transitory processor-readable media may compriseRAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic diskstorage or other magnetic storage devices, or any other tangible storagemedium that may be used to store desired program code in the form ofinstructions or data structures and that may be accessed by a computeror processor. Disk and disc, as used here, include compact disc (CD),laser disc, optical disc, digital versatile disc (DVD), floppy disk, andBlu-ray disc where disks usually reproduce data magnetically, whilediscs reproduce data optically with lasers. Combinations of the aboveshould also be included within the scope of computer-readable media.Additionally, the operations of a method or algorithm may reside as oneor any combination or set of codes and/or instructions on anon-transitory processor-readable medium and/or computer-readablemedium, which may be incorporated into a computer program product.

The preceding description of the disclosed embodiments is provided toenable any person skilled in the art to make and use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedhere may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown here but is to beaccorded the widest scope consistent with the following claims and theprinciples and novel features disclosed here.

What is claimed is:
 1. A method for controlling a start of ametalworking operation comprising: detecting an initial contact betweena wire being fed from a wire feeding apparatus and a workpiece; inresponse to the detection, halting feeding of the wire from the weldingapparatus; with the wire in contact with the workpiece, activating ahigh energy heat source configured to heat a tip of the wire to asoftened state; and after application of the high energy heat source isactivated, resuming the feeding of the wire from the wire feedingapparatus, wherein, the feeding of the wire is resumed by measuring aforce feedback from the wire contacting the workpiece.
 2. The method ofclaim 1, wherein after initial contact of the wire with the workpieceand prior to activating the high energy heat source configured to heat atip of the wire to a plastic state, the wire is subjected to preliminaryheating with another energy source.
 3. The method of claim 1, afterinitial contact of the wire with the workpiece and prior to activatingthe high energy heat source configured to heat a tip of the wire to aplastic state, the wire is subjected to resistive heating with anotherenergy source.
 4. The method of claim 1 wherein the initial contact isdetected based on the force feedback.
 5. The method of claim 2 whereinthe plastic state is detected when the force feedback from the wire isreduced below a force corresponding to the detection of the initialcontact.
 6. The method of claim 1 wherein the high energy heat source isa laser.
 7. The method of claim 1, wherein the high energy heat sourceis a plasma.
 8. The method of claim 1 further comprising: determining,by circuitry including control circuitry, a force error for the forcefeedback based on a predetermined force threshold; and adjusting, by thecircuitry, heating of the wire, a feed rate of the wire, or both basedat least in part on the force error when the force error is outside ofthe predetermined force threshold.
 9. The method of claim 1 furthercomprising maintaining, by the circuitry, a constant wire feed speedafter resuming the feeding of the wire.
 10. The method of claim 1wherein the force feedback is measured directly via a force measurementdevice.
 11. The method of claim 10, wherein the force feedback ismeasured using a load cell or a dynamometer.
 11. The method of claim 1wherein the force feedback is inferred based on a change in a feed motorcurrent of the wire feeding apparatus.
 12. The method of claim 11wherein the control circuitry varies the feed motor current to maintaina constant wire feed speed.
 13. The method of claim 8 furthercomprising: increasing, by circuitry including a control circuitry, theheating current when the force error is above the predetermined forcethreshold; and decreasing, by the circuitry, the heating current whenthe force error is below the predetermined force threshold.
 14. Ametalworking apparatus comprising: a wire feed mechanism configured tofeed a wire from a gun onto a workpiece; a heating power supplyconfigured to supply a heating current to the wire; and circuitryconfigured to (a) detect an initial contact between the wire being fedfrom the welding gun and the workpiece, (b) in response to thedetection, halt feeding of the wire from the welding gun, (c) activate ahigh energy heat source configured to heat a tip of the wire, and (d)resume the feeding of the wire from the welding gun when the tip of thewire is heated by the high energy heat source to a softened state,wherein, the feeding of the wire is resumed by measuring a forcefeedback from the wire contacting the workpiece.
 15. The apparatus ofclaim 14 wherein the initial contact is detected based on the forcefeedback.
 16. The apparatus of claim 15 wherein the plastic state isdetected when the force feedback from the wire is reduced below a forcecorresponding to the detection of the initial contact.
 17. The apparatusof claim 14 wherein the high energy heat source is a laser.
 18. Theapparatus of claim 14 wherein the high energy heat source is a plasma.19. The apparatus of claim 14 wherein the circuitry is furtherconfigured to: determine a force error for the force feedback based on apredetermined force threshold; and adjust the heating of the wire basedat least in part on the force error when the force error is outside ofthe predetermined force threshold.
 20. The apparatus of claim 14 whereinthe circuitry is further configured to maintain a constant wire feedspeed or constant ramp rate after resuming the feeding of the wire. 21.The apparatus of claim 14 further comprising a force measurement devicethat directly measures the force feedback.
 22. The apparatus of claim21, wherein the force measurement device is a load cell or adynamomoter.
 23. The apparatus of claim 14 wherein the force feedback isinferred based on a change in a feed motor current of the wire feedmechanism.
 24. The apparatus of claim 23 wherein the circuitry isfurther configured to vary the feed motor current to maintain a constantwire feed speed.
 25. The apparatus of claim 19 wherein the circuitry isfurther configured to: increase the heating current when the force erroris above the predetermined force threshold; and decrease the heatingcurrent when the force error is below the predetermined force threshold.26. The method of claim 8, wherein the control circuitry implements aconstant torque control scheme.
 27. The apparatus of claim 20, whereinthe circuitry implements a constant torque control scheme.